[Pw_forum] What's wrong in my calculation of epsilon of fcc Au?

[gbliu]

Dear Sun,

    Thanks for your reply.  I know this. Automatic k-mesh is only used 
in the scf run. In the following *nscf *run I used a self defined 
k-mesh,  which can be seen in the attached file fccAu.nscf4eps.in of the 
original mail.

Best regards,
Liu Gui-Bin

? 2011/7/7 23:53, Tao Sun ??:
> Hi.
>
> I have never done dielectric function calculations.  But the kmesh you
> are using "15 15 15 1 1 1" automatic seems to be inconsistent with
> this manual.  https://ir.library.dc-uoit.ca/bitstream/10155/159/3/McNelles_Phillip_appendixA.pdf.
>    Maybe this is worth checking, i.e. set the full kmesh by hand,
> without symmetry.
>
> Best
>
> Tao
>
> On Thu, Jul 7, 2011 at 4:39 AM, gbliu<goodluck_1982 at 163.com>  wrote:
>> Dear all,
>>
>>       I want to calculate dielectric function of carbon nanotube, but I have
>> no experiences of calculating dielectric function before. Hence, I decide to
>> start with a simple case of fcc gold, because there are referable results
>> from wien2k (wien2k is capable of simple case such as fcc Au, but too
>> resource consumptive to deal with large cells such as CNT).
>>       Because epsilon.x doesn't support USPP, the UPF file of Au is got by
>> converting fhi file from abinit using fhi2upf.x. I calculate fcc Au with
>> a=7.71bohr and 15x15x15 k-mesh using both pwscf(v4.3) and wien2k. First I
>> check the band structures and find that the results from both softwares
>> agree well (see attachments). But the results of epsilon from pwscf is not
>> satisfactory as the results from wien2k:
>>
>>       (1) Figures imag_eps and real_eps are the compares with only interband
>> contribution. (note that for pwscf, I subtract the intraband contribution
>> [-omega_p^2/omega^2] to get only interband contribution for compares). We
>> can see the differences are notable. What's the reason?/*  */_*BTW, I use a
>> homogeneous k-mesh also 15x15x15 generated by myself for epsilon calculation
>> (see input file fccAu.nscf4eps.in).*_
>> ------input for epsilon.x--------
>> &inputpp
>>      outdir='./work'
>>      prefix='fccAu'
>>      calculation='eps'
>> /
>> &energy_grid
>>      smeartype='gauss'
>>      intersmear=0.1d0
>>      intrasmear=0d0
>>      wmax=20d0
>>      wmin=0d0
>>      nw=600
>>      shift=0d0
>> /
>> --------------------------------
>>
>>      (2) As for the intraband contribution, wien2k gives the plasma frequency
>> 9.0075eV which agrees well with experimental value (ref:
>> http://wave-scattering.com/drudefit.html), but the result from epsilon.x is
>> puzzling.
>> Specifically, plasma frequency given in the output of epsilon.x is dependent
>> on the input parameters:
>> <1>. intrasmear=0,   wmax=20d0  -->     The bulk xx plasmon frequency [eV] is:
>>     14.877926200
>> <2>. intrasmear=0,   wmax=10d0  -->     The bulk xx plasmon frequency [eV] is:
>>     7.625822195
>> <3>. intrasmear=0,   wmax=6d0   -->     The bulk xx plasmon frequency [eV] is:
>>     3.156554381
>> <4>. intrasmear=0.1, wmax=20d0  -->     The bulk xx plasmon frequency [eV] is:
>>     15.766403193
>> <5>. intrasmear=0.1, wmax=10d0  -->     The bulk xx plasmon frequency [eV] is:
>>     9.322251787
>> <6>. intrasmear=0.1, wmax=20d0  -->     The bulk xx plasmon frequency [eV] is:
>>     6.263713572
>> However, none of these values is the one got by fitting the results using
>> Drude model [ 1 - omega_p^2/(omega^2+i*omega*gamma), gamma is the intrasmear
>> here ]. By fitting the results using Drude model, I get omega_p=5.528769eV,
>> for all the cases above (<1>~<6>). But this omega_p is far from the
>> experimental value (~9 eV)! What's wrong? And what are the meanings of the
>> values given in<1>~<6>  ?
>>
>>       How can I get more accurate results like the ones from wien2k?
>>       Please help me if you know something about this, thanks in advance!
>>
>> Best regards!
>>
>>                    Liu Guibin
>>                Postdoctoral Fellow,
>>                Department of Physics,
>>                The University of Hong Kong
>>                gbliu at hku.hk
>>
>>
>>
>>
>>
>>
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